Heat pipe with axial wick

ABSTRACT

A heat pipe has an evaporator portion, a condenser portion, and at least one flexible portion that is sealingly coupled between the evaporator portion and the condenser portion. The flexible portion has a flexible tube and a flexible separator plate held in place within the flexible tube so as to divide the flexible tube into a gas-phase passage and a liquid-phase artery. The separator plate and flexible tube are configured such that the flexible portion is flexible in a plane that is perpendicular to the separator plate.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Contract No.NASW-4884 awarded by the National Aeronautics and Space Administration(NASA). The government has certain rights in the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

BACKGROUND

1. Field

The present invention generally relates to heat-transfer systems and, inparticular, to a bendable heat pipe having an axial wick insert.

2. Description of the Related Art

In conventional heat pipes, a liquid-phase working fluid is provided toan evaporator whereupon the working fluid extracts heat from theevaporator and is converted to a vapor-phase by evaporation. Thevapor-phase working fluid is conveyed to a condenser wherein the workingfluid rejects hear to a heat sink by condensation and is therebyreturned to the liquid-phase.

Some conventional heat pipes, particularly heat pipes intended for usein low-gravity environments utilize arteries, i.e. channels, to providecapillary pressure to circulate the liquid-phase working fluid from thecondenser to the evaporator. Some low-gravity heat pipes providearterial wicks wherein the arteries carrying the liquid-phase workingfluid are separated from the gas-phase region by a capillary-scale slotor a fine-weave mesh. Conventional arterial heat pipes, however, aresusceptible to bubble-induced failures and, in addition, may fail toprime properly in a low-gravity environment. Bubbles may form in theliquid working fluid, such bubbles being particularly persistent in thepresence of non-condensable gases, i.e. gases other than the heat pipeworking fluid, that may be present as impurities or may evolve bychemical reaction during operation of the heat pipe.

Certain conventional arterial heat pipes may provide one or more wicksas an insert within the gas-phase region of the heat pipe. Wick insertshaving machined structures may have limited flexibility, therebypresenting a challenge for use in deployable heat management systems,and inserted wick inserts having porous structures may havesubstantially lower heat transport capabilities, thereby presenting achallenge for use in a high-performance system such as may be requiredon space vehicles.

SUMMARY

The present invention generally relates to heat-transfer systems and, inparticular, to a bendable heat pipe having an axial wick insert.

It is desirable to provide a high-transport heat pipe for use in alow-gravity environment without sensitivity to blockage of liquidarteries by gas bubbles. It may also be desirable to provide ahigh-transport heat pipe having a flexible portion(s) allowing fordeployment of one or more attached sections such as a radiator assemblycoupled to the condenser portion. It may also be desirable to providesuch a heat pipe to provide mechanical isolation between elements ofsensitive instruments. In an example envisioned application, a deployedradio frequency (RF) payload wing may transfer excess heat through aflexible heat pipe to the spacecraft radiators.

In certain embodiments, a heat pipe is disclosed that includes anevaporator portion, a condenser portion, and at least one flexibleportion sealingly coupled between the evaporator portion and thecondenser portion. The at least one flexible portion includes a flexibletube having a plurality of inner contact points and a flexible separatorplate comprising two lateral edges that are disposed proximate to theinner contact points of the tube so as to divide the interior volumeinto a gas-phase passage and a liquid-phase artery. The separator platehas a first plane that passes through the two lateral edges when theseparator plate is flat. The separator plate and flexible tube areconfigured such that the at least one flexible portion is flexible atleast in a second plane that is perpendicular to the first surface.

In certain embodiments, an evaporator portion of a heat pipe isdisclosed that includes a tube comprising an interior volume with aninner surface and a centerline, a separator plate disposed within thetube and comprising two lateral edges that are proximate to the innersurface of the tube so as to divide the interior volume into a gas-phasepassage and a liquid-phase artery, and a vent hole formed through theseparator plate so as to connect the gas-phase passage to theliquid-phase artery. The vent hole has a diameter that is greater thanor equal to a diameter of the largest circle that can be inscribedwithin the liquid-phase artery in a cross-section of the tube takenperpendicular to the centerline.

In certain embodiments, an evaporator portion of a heat pipe isdisclosed that includes a tube comprising an interior volume with aninner surface and a separator plate disposed within the tube andcomprising two lateral edges that are proximate to the inner surface ofthe tube so as to divide the interior volume into a gas-phase passageand a liquid-phase artery. The separator plate includes a plurality oftabs projecting toward the gas-phase passage from both of the lateraledges of the separator plate. Each tab has a tip that is proximate tothe inner surface of the tube. The tabs are configured to urge theseparator plate downward so as to maintain the two lateral edgesproximate to the inner surface of the tube.

In certain embodiments, an evaporator portion of a heat pipe isdisclosed that includes a tube comprising an interior volume with aninner surface, a separator plate disposed within the tube and comprisingtwo lateral edges that are proximate to the inner surface of the tube soas to divide the interior volume into a gas-phase passage and aliquid-phase artery, and a splitter disposed within the liquid-phaseartery in contact with the separator plate and the inner surface of thetube so as to divide the liquid phase artery into a plurality ofliquid-phase subarteries.

In certain embodiments, a condenser portion of a heat pipe is disclosedthat includes a tube comprising an interior volume with an inner surfaceand a separator plate disposed within the tube, the separator platecomprising two lateral edges that are proximate to the inner surface ofthe tube so as to divide the interior volume into a gas-phase passageand a liquid-phase artery. The separator plate also has a first portionhaving a constant size of the gas-phase passage and a second portionthat is inclined within the tube and configured such that the gas phasepassage becomes larger toward an outermost end of the tube.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide furtherunderstanding and are incorporated in and constitute a part of thisspecification, illustrate disclosed embodiments and together with thedescription serve to explain the principles of the disclosedembodiments. In the drawings:

FIG. 1 depicts a spacecraft using a conventional fixed heat piperadiator.

FIG. 2 depicts a deployable radiator that is coupled to a plurality ofexemplary heat pipes according to certain aspects of the presentdisclosure.

FIG. 3 is a perspective view of an exemplary heat pipe according tocertain aspects of the present disclosure.

FIG. 4 is a perspective view of an exemplary wick insert according tocertain aspects of the present disclosure.

FIG. 5 is a cutaway view of the flexible portion of the heat pipe ofFIG. 3 in both the straight and flexed positions according to certainaspects of the present disclosure.

FIGS. 6A-6D are cross-sectional views of the heat pipe of FIG. 3according to certain aspects of the present disclosure.

FIG. 6E is an enlargement of a detail F-F of FIG. 6B according tocertain aspects of the present disclosure.

FIG. 7 is a cutaway view of a portion of the condenser portion of theheat pipe of FIG. 3 according to certain aspects of the presentdisclosure.

FIGS. 8A-8C are cross-sectional views of an example heat pipeillustrating the movement of the working fluid according to certainaspects of the present disclosure.

FIGS. 9A-9B are cross-sections of an example evaporation portion of aheat pipe showing the size of inscribed circles within the liquid-phasearteries according to certain aspects of the present disclosure.

FIGS. 10A-10B are cross-sectional side views of the example heat pipeillustrating exemplary vent holes according to certain aspects of thepresent disclosure.

FIG. 11 depicts an alternate configuration of a heat pipe according tocertain aspects of the present disclosure.

FIGS. 12A-12C depict an exemplary configuration of a wick insert withina bellows tube in a flexible portion of a heat pipe according to certainaspects of the present disclosure.

FIGS. 13A-13B depict another embodiment of a flexible wick insert thatcan be bent in multiple directions according to certain aspects of thepresent disclosure.

DETAILED DESCRIPTION

The present invention generally relates to heat-transfer systems and, inparticular, to a bendable heat pipe having an axial wick insert.

The following description discloses embodiments of a heat pipe that isparticularly adapted for use on a spacecraft in a low-gravityenvironment. In certain embodiments, the heat pipe includes a flexiblesection allowing a radiator assembly to be deployed thereby improvingthe heat rejection capability of the radiator assembly.

The detailed description set forth below is intended as a description ofvarious configurations of the subject technology and is not intended torepresent the only configurations in which the subject technology may bepracticed. The appended drawings are incorporated herein and constitutea part of the detailed description. The detailed description includesspecific details for the purpose of providing a thorough understandingof the subject technology. However, it will be apparent to those skilledin the art that the subject technology may be practiced without thesespecific details. In some instances, well-known structures andcomponents are shown in block diagram form in order to avoid obscuringthe concepts of the subject technology. Like components are labeled withidentical element numbers for ease of understanding.

FIG. 1 depicts a spacecraft 10 using a conventional fixed heat piperadiator 12. The radiator 12 can reject heat in only a single directionaway from the body of the spacecraft 10, as the opposite side of theradiator 12 is facing the spacecraft itself.

FIG. 2 depicts a deployable radiator 50 that is coupled to a pluralityof exemplary heat pipes 100 according to certain aspects of the presentdisclosure. The radiator 50 is part of a heat management system 40 ofthe spacecraft 20. The flexible heat pipes 100 enable the condenserportion 110 to extend away from a stowed position to a deployed positionextending away from the spacecraft. The radiator 50 is stowed in recess22 at launch and then deployed after the spacecraft 20 is in orbit. Theheat pipes 100 each comprise a condenser portion 110 coupled toradiation panels 52 on both sides, where the panel 52 on the near sidehas been cut away to reveal the condenser portions 110. The radiatorpanels 52 are configured to distribute the heat from the condenserportions 110 across the surface of the panel 52 and effectively radiatethe heat to an external heat sink, for example deep space, usingprinciples known to those of skill in the art. With a panel 52 on eachside, the heat rejection capability of the radiator 50 may be greaterthan the single-sided radiator 12 of FIG. 1. The heat pipes 100 eachalso comprise an evaporator portion 130 coupled to a cold plate 54 onboth sides, in this example, where the panel 54 on the near side hasbeen cut away to reveal the evaporator portions 130. The panels 54absorb heat from internal components (not shown in FIG. 2) and transferthe heat to the evaporator portions 130. The condenser portions 110 andevaporator portions 130 are connected by flexible portions 120, theconstruction of which is discussed in greater detail with respect toFIG. 5.

FIG. 3 is a perspective view of an exemplary heat pipe 100 according tocertain aspects of the present disclosure. The heat pipe 100 comprises acondenser portion 110, a flexible portion 120, and a evaporator portion130, with end caps 140 sealing the outer ends of the condenser portion110 and the evaporator portion 130. Each of the condenser portion 110and the evaporator portion 130 have an outer end and an inner end,wherein the inner end is closest to the other of the condenser portion110 and the evaporator portion 130. In certain embodiments, thecondenser portion 110 and the evaporator portion 130 comprise an outertube 112, 132 that, together with the flexible portion 120, provide asingle axial chamber that is, in certain embodiments, generally circularin cross-section. In certain embodiments, the tubes 112, 132 may becrimped and sealed in place of an end cap 140. The internal constructionof the various portions 110, 120, and 130 is discussed below. Thesurfaces 114 and 134 are adapted to be thermally coupled to the panels52 and 54, respectively, when the heat pipe 100 is assembled into a heatmanagement system such as system 40 of FIG. 2. The labels A-A throughD-D indicate the locations of cross-sectional views of FIGS. 6A-6D,respectively.

FIG. 4 is a perspective view of an exemplary wick insert 150 accordingto certain aspects of the present disclosure. In this embodiment, thewick insert comprises two elements 152 and 154. Element 152 comprises aseparator plate 160 and a plurality of tabs 162 extending from a lowertab portion 164 on each side of the separator plate 160. Element 154comprises a similar separator plate 161 and a plurality of tabs 163extending from a lower tab portion 165 on each side of the separatorplate 161. The wick insert element 154 comprises an inclined portion161A and extended tabs 163A, which are discussed in greater detail withrespect to FIG. 7. In this example, the separator plate 160 of element152 comprises an extension 160A that will be disposed within theflexible portion 120 when the heat pipe 100 is assembled. In certainembodiments, the extension 160A does not have the lower tab portion 164or the tabs 162. In certain embodiments, the extension 160A extends intothe evaporator portion 130 when the heat pipe 100 is assembled andoverlaps the separator plate 161 of the element 154. The function ofthis overlap is discussed in greater detail with respect to FIG. 5. Incertain embodiments, the elements 152 and 154 each comprise attachmenttabs 180 configured to be attached to the flexible portion 120 so as tolocate the wick insert 150 with respect to the flexible portion 120 andprevent displacement of the wick insert 150 as the heat pipe 100 bends.The attachment of attachment tabs 180 is discussed in greater detailwith respect to FIG. 6C. Vent holes 170 are visible in the separatorplate 160 of the evaporator condenser portion 110, and are discussed ingreater detail with respect to FIGS. 10A & 10B. The labels E-E indicatethe location of the cross-sectional view shown in FIG. 7. A wick insert150 may be particularly advantageous for use with outer tubes 112, 132that are made from certain metals, e.g. nickel and Invar, that cannoteasily be extruded with lengthwise grooves, such as shown in FIG. 11, tolocate a wick insert.

FIG. 5 is a cutaway view of the flexible portion 120 of the heat pipe100 of FIG. 3 in both the straight and flexed positions according tocertain aspects of the present disclosure. The example flexible portion120 comprises a bellows tube 190 coupled to a collar 194 at each end. Incertain embodiments, the outer tubes 112, 132 of the condenser portion110 and evaporator portion 130 are also coupled to the collars 194 whenthe heat pipe 100 is assembled, thereby forming the sealed single axialchamber 200. In certain embodiments, the bellows tube 190 comprises aplurality of radially outward extending convexly curved elements alongthe length of the bellows tube 190 which are connected to each other byconcavely curved inner portions, i.e. individual bellows. In certainembodiments, the flexible portion 120 comprises a surrounding braidedsleeve 192 that is also coupled to the collars 194.

The wick insert elements 152 and 154 are disposed within the outer tubes112 and 132, respectively, and the wick insert element 152 extendsthrough the bellow tube 190 and into the outer tube 132 where extension160A overlaps the separator plate 161 of the wick insert 154. The wickinserts 152, 154 acts as barrier to form two distinct passages withinthe outer tubes 112, 132 and bellows tube 190. As the flexible portion120 moves from the straight position to the flexed position, theelements of the flexible portion 120 bend about a neutral axis 151.Elements that are on an outer side of the neutral axis 151 will tend tostretch while elements that are on an inner side of the neutral axis 151will tend to compress. As the separator plates 160, 161 are on the outerside of neutral axis 151, the separator plate 160 will pull away fromthe separator plate 161. The overlap of the extension 160A with theseparator plate 161 maintains the continuity of the separator plates160, 161 along the single axial chamber 200. The ability to maintain thecontinuity of the separator plates 160, 161, and therefore maintain theseparation of the portions of the single axial chamber 200 that areabove and below the separations plates 160, 161, is one feature thatallows the assembled heat pipe 100 to be bent after fabrication whilemaintaining its heat transfer capability.

In the example embodiment, a spring 196 is disposed inside andconstrained by the bellows 190 in the vapor-phase portion of the singleaxial chamber 200. The spring 196 is also constrained by the wick insertelement 152. The spring 196 enables the wick insert element 152 todeform during flexure without buckling. As shown in FIG. 5, in theflexed position the bellows 190 and the spring 196 are bent so that attheir radial edges the bellows 190 have a compressed inner side and anexpanded outer side near the inner walls of the braided sleeve 192.Similarly, the spring 196 has an expanded radial edge and a compressedradial edge. As depicted in FIG. 5, the expanded spring radial edge isdisposed against the separator plate 160 of the wick insert element 152and the compressed spring radial edge is disposed against the bellows190 inner diameter. It will be apparent to those of skill in the artthat the flexible portion 120 may also be bent in the opposite mannerwhere the expanded spring radial edge is disposed against the bellows190 inner diameter and the compressed spring radial edge is disposedagainst the separator plate 160.

FIGS. 6A-6D are cross-sectional views of the heat pipe 100 of FIG. 3according to certain aspects of the present disclosure. FIG. 6A showsthe wick insert element 152 disposed within the outer tube 112 atlocation A-A. The wick insert 152 in the condenser portion 110 may begraded by the use of a splitter 115 that separates the liquid passageinto two or more distinct sub-passages 202 and 203. The wick insert 152contacts the inner wall of the outer tube 112, which comprises grooves113, at the lateral corners of the separator plate 160 and the tips ofthe tabs 162 and the divider 115. The contact between the corners of theseparator plate 160 and the grooves 113 is discussed in greater detailwith respect to FIG. 6E. In operation, there will be a gas-phase flow220 in the gas-phase passage 201 that is above the separator plate 160and liquid-phase flows 225 and 230 in the arteries 202 and 203,respectively. The separator plate 160 has vent holes 172 in the regionover the divider 115. Vent holes should have a diameter that is greaterthan or equal to the capillary pumping dimension of the liquid passage,which may be characterized by either the hydraulic diameter or thelargest circle that can be inscribed within a cross-section of theliquid passage taken perpendicular to the tube centerline. Vent holes172 are discussed in greater detail with respect to FIGS. 9A and 10A.

The use of splitter 115 increases the capillary pressure difference,i.e. capillary pumping, between liquid flows in sub-passages 202 and 203and the vapor flow in gas-phase passage 201 compared to a singlecombined passage such as shown in FIG. 6B. The smaller liquid-phasearteries 202, 203 permit the use of smaller vent holes 172, compared tothe vent hole 174 of a single liquid-phase artery. The capillarypressure is inversely proportional to the capillary pumping radius,where the capillary pumping radius is the maximum radius of curvature ofthe meniscus formed between the vapor and liquid phases. As the largestradius is typically at the vent holes 172, 174, the size of the venthole determines the local capillary pressure. The increase in capillarypressure more than offsets the increased flow resistance caused by thereduction in flow area of a liquid-phase artery 202 compared to the areaof a single liquid-phase artery. By placement of one or more suchsplitters 115, the performance of the heat pipe 100 may be optimized forany set of temperature, fluid and geometric constraints.

FIG. 6B shows the wick insert element 152 disposed within the outer tube112 at location B-B. In the heat pipe 100 of FIG. 3, the divider 115does not extend the full length of the condenser 110 and is not presentat location B-B, leaving a single liquid-phase artery 204 that is influid communication with the arteries 202 and 203. In operation, thereis a liquid-phase flow 235 that will divide into flows 225 and 230 whenthe flow 235 reaches the divider 115. In the region where there is nodivider 115, the separator plate 160 has vent holes 174, which may belarger than the vent holes 172, that are discussed in greater detailwith respect to FIGS. 9B and 10B. The labels F-F indicate the locationof the enlarged view of FIG. 6E.

FIG. 6C depicts the attachment of the attachment tabs 180 of the wickinsert element 154 to the outer tube 132 of the evaporator portion 130by, for example, spot welds 182. Also visible is the extension 160Athat, in this example, is underneath the separator plate 161 such thatthat extension 160A is captured between the inner wall of the outer tube132 and the separator plate 161.

FIG. 6D is a combination of a cross-sectional view and a cutaway view ofthe portion of the evaporator portion 130 beyond location D-D. The outertube 132 has grooves 133 on the inner wall, similar to the grooves 113of outer tube 112. Beyond location D-D, the separation plate 161 has aninclined portion 161A that tapers in width to maintain contact with thegrooves 133. As the inclined portion 161A of the separator plate 161descends, the tabs 163A must be longer than tabs 163 to maintain contactat their tips with the inner wall of the outer tube 132. The inclinedportion 161A of the separator plate 161 is discussed in greater detailwith respect to FIG. 7.

FIG. 6E is an enlargement of a detail F-F of FIG. 6B according tocertain aspects of the present disclosure. In certain embodiments, theinner wall of the outer tube 112 comprises generally circumferentialgrooves 113. In certain embodiments, the grooves 113 are formed in aspiral pattern. In certain embodiments, the grooves have a depth “t,”for example 0.13 mm (0.005 in.), chosen to transport the liquid-phaseworking fluid from the liquid-phase artery, for example artery 235 ofFIG. 6B, around the entire circumference of the gas-phase passage 201 bycapillary action of the working fluid. The separator plate 160 compriseslateral corners 166 that are generally in contact with the tops of thegrooves 113 such that the only passages connecting the liquid-phasepassages and the gas-phase passage 201 within the condenser portion 110are the grooves 113. In certain embodiments, there may be a gap betweena lateral corner 166 and one or more of the peaks of the grooves 113,wherein the gap is on the same order of magnitude as the grooves 113 andless than the diameter of the vent holes 172, 174 that are proximate tothe particular gap. Similarly, the evaporator portion 130 has grooves133 on the inner wall of the outer tube 132 and the correspondingcorners 166 of the separator plate 161 are in contact with the tops ofthe grooves 133 such that the grooves 133 form the only passagesconnecting the liquid-phase passage 235 and the gas-phase passage 201within the condenser portion 130.

FIG. 7 is a cutaway view of a portion of the evaporator portion 130 ofthe heat pipe 100 of FIG. 3 according to certain aspects of the presentdisclosure. At the outermost end of the evaporator portion 130, aninclined portion of the separator plate 161A is tapered thereby forminga gradually larger gas-phase passage 201. The end and sides of thetapered/inclined portion of the separator plate 161A are held againstthe inner walls of the outer tube 132 by the longer tabs 163A. Thistapered portion of the separator plate 161A permits the enlargement of aliquid slug 150 that is disposed within the end of the corner evaporatorportion 130. This enlargement of the liquid slug 150 reduces the zero-gcapillary back-pressure, since the capillary pressure is inverselyproportional to the radius of curvature of the meniscus 252 formed bythe liquid slug 250 in the gas-phase passage 201. The increased pressuredrop caused by the reduction of area in the liquid-phase artery 204under the inclined portion of the separator plate 161A is more thanoffset by the increased net capillary pressure resulting from the largerradius of the meniscus 252. Such tapering may be optimized based on netheat pipe performance requirements using a variety of taperconfigurations. In certain embodiments, the inclined portion 161A has anoutermost tip 167 that is in contact with the inner surface of the outertube 132 such that the liquid-phase artery 204 is terminated at theoutermost tip of the inclined portion 161A.

FIGS. 8A-8C are cross-sectional views of an example heat pipe 300illustrating the movement of the working fluid according to certainaspects of the present disclosure. In the evaporator portion 310, shownin the left portion of FIG. 8A, the heat transferred to the heat pipefrom the external heat source causes the liquid working fluid 350, whichhas followed the circumferential grooves 311 of the tube 312 to coverthe inner surface of the gas-phase passage 360, to evaporate whichincreases the pressure of the gaseous working fluid 351 in theevaporator portion 310 thereby causing the gaseous working fluid 351 toflow towards the condenser portion 330 as indicated by the arrowslabeled “VAPORS.” In the condenser portion 330, the flow of heat out ofthe condenser portion 330, for example into the radiation panels 52 ofFIG. 2, causes the gaseous working fluid 351 to condense on the grooves331 of the tube 332 into the liquid working fluid 350 and flow along thegrooves 331 into the liquid-phase artery 370. Capillary pressuredifferences cause the liquid working fluid 350 to flow in theliquid-phase artery 370 towards the evaporator portion 310. Bubbles 357of non-condensable gases (NCGs) that form in the liquid working fluid350 may escape into the gas-phase passage 360 via either the largerholes 380 or the smaller holes 385 located over a divider (not visiblein FIG. 8A) at the outer end of the evaporator portion 310.

FIG. 8B is a cross-sectional view of the heat pipe 300 at location 8B-8Bshown in FIG. 8A, with the view of FIG. 8B taken at right angles to theview of FIG. 8A. The gaseous working fluid 351 is passing along thegrooves 311 from the liquid-phase artery 370 past the separation plate160 into the gas-phase passage 360 as well as evaporating directly fromthe grooves on the inner wall of the gas-phase passage 360.

FIG. 8C is a cross-sectional view of the heat pipe 300 at location 8C-8Cshown in FIG. 8A, with the view of FIG. 8C taken at right angles to theview of FIG. 8A. The liquid working fluid 350 is passing from the wallsof the gas-phase passage 360, where the gaseous working fluid 351condensed, along the grooves 331 past the separation plate 161 into theliquid-phase artery 370.

FIGS. 9A-9B are cross-sections of an example evaporation portion 410 ofa heat pipe 400 showing the size of inscribed circles within theliquid-phase arteries 402, 403 according to certain aspects of thepresent disclosure. FIG. 9A depicts an outer tube 412 with a wick insert452 having a separation plate 462 forming a gas-phase passage 401 and asingle liquid-phase artery 402. The largest circle that can be inscribedwithin the cross-sectional area of the liquid-phase artery 402 is shownas the dashed-line circle 440.

When the wick insert 452 is installed into the tube 412, the tips of theplurality of tabs 462 are displaced inward while in contact with theinner surface of the tube 412 such that reaction forces 453 applied bythe tube to the tips of the plurality of tabs 462 together provide a netdownward force 454 on the wick insert 452. This downward force serves tomaintain the lateral edges 466 in contact with or proximate to the innersurface of the tube 412.

FIG. 9B depicts an evaporation portion 410A similar to the evaporationportion 410 of FIG. 9A with the addition of a divider 415 disposedbeneath separation plate 462 so as to form two separate liquid-phasearteries 403 that are, in this example, of equal size. In certainembodiments, the liquid-phase arteries may be of different sizes. Thelargest circles that can be inscribed within the cross-sectional area ofeach of the liquid-phase arteries 403 are shown as the dashed-linecircles 442, which are smaller than the circle 440 for a comparableconfiguration of a separator plate 460 within a tube 412.

FIGS. 10A-10B are cross-sectional side views of the example heat pipe400 illustrating exemplary vent holes 472, 474 according to certainaspects of the present disclosure. FIG. 10A corresponds to theevaporation portion 410 of FIG. 9A, having a single liquid-phase artery402. The largest spherical bubble 480 that can form in the liquid-phaseartery 402 will be approximately equal to the largest inscribed circle440 depicted in FIG. 9A. In order to reliably release the bubble 480into the gas-phase passage 401 before the bubble 480 becomes elongated,i.e. the bubble 480 becomes longer along the liquid-phase artery 402that the bubble 480 is wide, the vent hole 472 must be is greater thanor equal to the capillary pumping dimension of the liquid-phase passage402, which may be characterized by either the hydraulic diameter of theliquid-phase artery 402 or the largest circle 440 that can be inscribedwithin a cross-section of the liquid-phase artery 402 of FIG. 9A. Once agenerally spherical bubble 480 touches both the inner wall of the outertube 412 and the separator plate 460, the bubble's resistance tomovement may increase significantly and may become fixed in theliquid-phase artery 402, thereby blocking the liquid-phase artery 402and causing the heat pipe 400 to function at a reduced level ofperformance or, if the bubble 480 completely blocks flow through theliquid-phase artery 402, to stop working altogether. In certainembodiments, the vent hole 472 is circular and the diameter of the venthole 472 must be greater than or equal to a diameter of the inscribedcircle 440. Multiple vent holes 472 may be placed along the liquid-phaseartery 402 to provide multiple opportunities for the bubble 480 to ventas the bubble 480 progresses down the liquid-phase artery 402, but asingle vent hole 472 may be sufficient, in certain embodiments, tomaintain proper heat pipe operation.

FIG. 10B corresponds to the evaporation portion 410A of FIG. 9B, havingtwo liquid-phase arteries 403 separated by a divider 415. Similar to theembodiment of FIG. 10A, the vent hole 474 must be at least the same sizeas the largest inscribed circle 442 of FIG. 9B in order to reliablyrelease the bubble 480 into the gas-phase passage 401 before the bubble480 becomes elongated within the liquid-phase arteries 403. In certainembodiments, the vent hole 474 is circular and the diameter of the venthole 474 must be greater than or equal to the capillary pumpingdimension of the liquid-phase arteries 403, which may be characterizedby either the hydraulic diameter of the liquid-phase arteries 403 or thelargest circle 442 that can be inscribed within a cross-section of theliquid-phase artery 403. In the graded configuration of FIG. 10B, eachseparate passage 403 must have at least one vent hole 474 to maintainoperability in the presence of gas bubbles 480. The diameters of thevent holes 474 may be smaller than the diameter of the vent hole 473 inthe single liquid-phase artery of FIG. 10A.

FIG. 11 depicts an alternate configuration of a heat pipe 500 accordingto certain aspects of the present disclosure. Two narrow and opposingindents 490 penetrate outwards into the walls 432 of one or both of thecondenser portion 110 and the evaporator portion 130. Each indent 490provides a relatively small gap on the container internal surface intowhich a wick insert 490 is placed and retained. In the evaporatorportion 130, the wick insert extension 492 may fit under the wick insert490, similar to the configuration of extension 160A and separator plate161 shown in FIG. 4, and into the same indents 490.

FIGS. 12A-12C depict an exemplary configuration of a wick insert 550within a bellows tube 590 in a flexible portion 520 of a heat pipeaccording to certain aspects of the present disclosure. FIG. 12A depictsa partial cutaway view of a flexible portion 520 of a heat pipe, showinga braided sleeve 592 surrounding a bellows tube 590 within which isdisposed a wick insert 550 and a spring 596, similar to the flexibleportion 120 of FIG. 5. The separator plate 560 of the wick insert 550separates the gas-phase passage 601 from the liquid-phase artery 604.The labels G-G indicate the location of the view of FIG. 12B.

FIG. 12B is a cross-sectional view of the complete flexible portion 520.The lateral corners 566 of the separator plate 560 are generally incontact with the inner edges 561 of the individual bellows that form thebellows tube 590, wherein this line of contact separates the gas-phasepassage 601 from the liquid-phase artery 604. The dashed-line circle 640represents the largest inscribed circle that can be formed within theliquid-phase artery 604, with the circle 640 having a diameter 641. Thelabels H-H indicate the location of the view of the flexible portion 520of FIG. 12B that is shown in FIG. 12C.

FIG. 12C is a cross-section view of the complete flexible section 520 ofFIG. 12A as indicated by the labels H-H in FIG. 12B. The corner 566 ofthe separator plate 560 is generally in contact with the inner edges561, thus creating an opening 650, one of which is shown as across-hatched area in FIG. 12C, on each side of each individual bellows,i.e. the individual convolution of the bellows tube 590 that connectsthe gas-phase passage 601 to the liquid-phase artery 604. The size ofthe opening 650 must be limited to have less effect on the pumpingcharacteristics of the liquid-phase artery 604 than the vent hole 562formed in the separation plate 560. While the vent opening 562 iscircular and have a minimum diameter equal or greater than the diameter641 of the inscribed circle 640 shown in FIG. 12B, in this example, theopening 650 is not a circular shape and so does not have a single“diameter.” The opening 650 does have a “hydraulic diameter,” however,and the effect of the opening 650 on the pumping characteristics of theliquid-phase artery 604 will be less than that of the vent hole 562having a diameter 641 if the hydraulic diameter of the opening 650 isless than the diameter 641. The thickness and depth of the individualbellows of the bellows tube 590 are therefore based at least partiallyon achieving a hydraulic diameter for the openings 650 that is less thanthe diameter 641 of largest circle 640 that can be inscribed in theliquid-phase artery 604.

FIGS. 13A-13B depict another embodiment of a flexible wick insert 700that can be bent in multiple directions according to certain aspects ofthe present disclosure. FIG. 13A is a perspective view of the wickinsert 700 that is comprises of a separation plate 710 with, in thisembodiment, vent holes 730 formed in the solid portions 712 on eitherside of the flexible portion 711. This embodiment includes several tabs720 spaced along the wick insert 700 that serve to hold the wick insertin place within a bellows tube, e.g. the bellows tube 590 of FIG. 12A,in place of the spring 596. In certain embodiments, the tabs 720 areused with a spring, e.g. the spring 596 of FIG. 12A. A portion 13B ofthe wick insert 700 is enlarged in FIG. 13B. In certain embodiments, thetabs 720 are welded to the separation plate 710. In certain embodiments,the tabs 720 may be coupled to the separation plate using otherattachment methods known to those of skill in the art, e.g. mechanicallyinterlocking, brazing, soldering, etc.

FIG. 13B shows a portion of the wick insert 700 where a plurality ofslots 714 alternately extend inward from the lateral edges 713 to createa serpentine form in the separation plate 710. The portions of theserpentine form that are aligned parallel to a centerline 740 of theseparation plate 710 have a first width 718. The portions of theserpentine form that are perpendicular to the centerline 740 have asecond width 716. In certain embodiments, the slots 714 extend past thecenterline 740. In certain embodiments, the first and second widths 718,716 are approximately equal. In certain embodiments, the first width 718is less than the second width 716. The slots 714 increase the lateralflexibility of the wick insert 700 in a plane that is parallel to theseparation plate 710 and passes through both lateral edges 713. Incertain embodiments, a flexible portion of a heat pipe that includes thewick insert 700 may be locally bent in any plane that passes through thecenterline 740. In certain embodiments, a flexible portion of a heatpipe that includes the wick insert 700 may be sequentially bent alongits length in different planes that each pass through the centerline740.

In certain embodiments, the portion of the wick insert 700 that islocated within a condenser portion or evaporator portion, e.g. sections110, 130 of heat pipe 100 in FIG. 3, may have slots 714 such that thecondenser portion or evaporator portion can be bent or formed into aparticular shape after assembly. The degree of flexibility and theminimum radius of curvature that can be achieved while bending eitherthe rigid condenser or evaporator portions or the flexible portion of aheat pipe may be a function of one or more of the spacing and the lengthof the slots.

The disclosed examples of a heat pipe are particularly suitable for usein a low-gravity environment. The use of vent holes having diametersthat are greater than or equal to the largest circle that can beinscribed in the liquid-phase artery located below the respective venthole reduces the likelihood of a gas bubble obstructing the artery byventing such gas bubbles before they become lodged in the artery. Theuse of dividers to create multiple small liquid-phase arteries in placeof a single, larger liquid-phase artery improves the heat transfercapability of a heat pipe by grading the pumping characteristics of theliquid-phase arteries.

This application includes description that is provided to enable aperson of ordinary skill in the art to practice the various aspectsdescribed herein. While the foregoing has described what are consideredto be the best mode and/or other examples, it is understood that variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. It is understood that the specific order or hierarchy ofsteps or blocks in the processes disclosed is an illustration ofexemplary approaches. Based upon design preferences, it is understoodthat the specific order or hierarchy of steps or blocks in the processesmay be rearranged. The accompanying method claims present elements ofthe various steps in a sample order, and are not meant to be limited tothe specific order or hierarchy presented. Thus, the claims are notintended to be limited to the aspects shown herein, but is to beaccorded the full scope consistent with the language claims.

Headings and subheadings, if any, are used for convenience only and donot limit the invention.

Reference to an element in the singular is not intended to mean “one andonly one” unless specifically so stated, but rather “one or more.” Useof the articles “a” and “an” is to be interpreted as equivalent to thephrase “at least one.” Unless specifically stated otherwise, the terms“a set” and “some” refer to one or more.

Terms such as “top,” “bottom,” “upper,” “lower,” “left,” “right,”“front,” “rear” and the like as used in this disclosure should beunderstood as referring to an arbitrary frame of reference, rather thanto the ordinary gravitational frame of reference. Thus, a top surface, abottom surface, a front surface, and a rear surface may extend upwardly,downwardly, diagonally, or horizontally in a gravitational frame ofreference.

Although the relationships among various components are described hereinand/or are illustrated as being orthogonal or perpendicular, thosecomponents can be arranged in other configurations in some embodiments.For example, the angles formed between the referenced components can begreater or less than 90 degrees in some embodiments.

Although various components are illustrated as being flat and/orstraight, those components can have other configurations, such as curvedor tapered for example, in some embodiments.

Pronouns in the masculine (e.g., his) include the feminine and neutergender (e.g., her and its) and vice versa. All structural and functionalequivalents to the elements of the various aspects described throughoutthis disclosure that are known or later come to be known to those ofordinary skill in the art are expressly incorporated herein by referenceand are intended to be encompassed by the claims. Moreover, nothingdisclosed herein is intended to be dedicated to the public regardless ofwhether such disclosure is explicitly recited in the claims. No claimelement is to be construed under the provisions of 35 U.S.C. §112, sixthparagraph, unless the element is expressly recited using the phrase“means for” or, in the case of a method claim, the element is recitedusing the phrase “operation for.”

A phrase such as an “aspect” does not imply that such aspect isessential to the subject technology or that such aspect applies to allconfigurations of the subject technology. A disclosure relating to anaspect may apply to all configurations, or one or more configurations. Aphrase such as an aspect may refer to one or more aspects and viceversa. A phrase such as an “embodiment” does not imply that suchembodiment is essential to the subject technology or that suchembodiment applies to all configurations of the subject technology. Adisclosure relating to an embodiment may apply to all embodiments, orone or more embodiments. A phrase such as an embodiment may refer to oneor more embodiments and vice versa.

The word “exemplary” is used herein to mean “serving as an example orillustration.” Any aspect or design described herein as “exemplary” isnot necessarily to be construed as preferred or advantageous over otheraspects or designs.

All structural and functional equivalents to the elements of the variousaspects described throughout this disclosure that are known or latercome to be known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe claims. Moreover, nothing disclosed herein is intended to bededicated to the public regardless of whether such disclosure isexplicitly recited in the claims. No claim element is to be construedunder the provisions of 35 U.S.C. §112, sixth paragraph, unless theelement is expressly recited using the phrase “means for” or, in thecase of a method claim, the element is recited using the phrase “stepfor.” Furthermore, to the extent that the term “include,” “have,” or thelike is used in the description or the claims, such term is intended tobe inclusive in a manner similar to the term “comprise” as “comprise” isinterpreted when employed as a transitional word in a claim.

Although embodiments of the present disclosure have been described andillustrated in detail, it is to be clearly understood that the same isby way of illustration and example only and is not to be taken by way oflimitation, the scope of the present invention being limited only by theterms of the appended claims.

What is claimed is:
 1. A heat pipe, comprising: an evaporator portion; acondenser portion; and at least one flexible portion sealingly coupledbetween the evaporator portion and the condenser portion, the at leastone flexible portion comprising: a flexible tube comprising an interiorvolume and a plurality of inner edges; and a flexible separator platecomprising two lateral edges that are disposed proximate to the inneredges of the tube, wherein the interior volume comprises a gas-phasepassage on a first side of the flexible separator plate and aliquid-phase artery on an opposing second side of the flexible separatorplate, the separator plate further comprising a first plane that passesthrough the two lateral edges when the separator plate is flat, whereinthe separator plate and flexible tube are configured such that the atleast one flexible portion is flexible in at least a second plane thatis perpendicular to the first plane, wherein the first plane comprises acenterline that is midway between the two lateral edges when theseparator plate is flat, wherein the flexible portion is flexible in anyplane that passes through the centerline of the separator plate, whereinthe evaporator portion comprises a separation plate, a gas-phasepassage, a liquid-phase artery, and a vent hole formed through theseparator plate so as to connect the gas-phase passage to theliquid-phase artery, the vent hole comprising a diameter that is greaterthan or equal to a diameter of the largest circle that can be inscribedwithin the liquid-phase artery in a cross-section of the evaporatorportion taken perpendicular to a centerline of the evaporator portion,wherein the flexible tube comprises a bellows tube that comprises aplurality of individual bellows each comprising an opening defined bythe lateral edge of the separation plate and an inner surface of theindividual bellows, and wherein each opening has a respective hydraulicdiameter that is less than the diameter of the vent hole.
 2. The heatpipe of claim 1, wherein: the first plane comprises a centerline that ismidway between the two lateral edges when the separator plate is flat;and the flexible portion is flexible in any plane that passes throughthe centerline of the separator plate.
 3. The heat pipe of claim 1,further comprising a coil spring disposed in the gas-phase passage ofthe flexible portion.
 4. The heat pipe of claim 3, wherein: the coilspring comprises a plurality of coils; at least one of the plurality ofcoils is in contact with at least one of the inner edges of the flexibletube; and at least one of the plurality of coils is in contact with theseparation plate.